The tuberculin skin test (TST) has been the traditional method of testing for the presence of latent TB infection (LTBI) in HCW in low incidence countries. The TST is subject to bias and errors in placement and reading, and repeated exposure to the antigen in the purified protein derivative may boost future responses to repeat TST. The TST must be read 48-72 hours after intradermal injection, problematic because of low subject compliance for follow-up. To reduce the prevalence of such testing errors, over the past eight years, healthcare institutions in low-incidence countries have employed an alternative to the TST for HCW, a blood test that uses an interferon-gamma release assay (IGRA).